This invention relates to an improvement of the weaving technique by which the weft thread is inserted into the shed formed by the warp threads without using any shuttle
It relates in particular to an improvement of the technique known under the name of "inertia insertion," which is described in the French Pat. No. 1,562,147 (corresponding to the U.S. Pat. No. 3,543,808).
In a general manner, the aforesaid technique consists in casting the weft thread into the shed formed by the warp threads in the shape of a loop having at one end a free end, called the "cast strand" which is cast at high speed in a specific direction, that is to say, inside the space between the two layers of warp threads forming the shed. At the other end of the loop is a second end called the "locked strand" which is held by a clip outside the space between the two layers of warp threads. Thus, the kinetic energy within the cast strand changes, inside the loop, into a force pulling the thread in the direction of the loop motion, this force may be stronger than the air resistance.
The expression "cast strand" shall be used hereinafter in the description to designate the end of the loop which is freely cast, whereas the expression "locked strand" shall be used to designate the other part of this loop of thread.
The cast strand motion is produced either by means of a lever with a pin or a pulley at its free end, simultaneously accelerating the loop and the thread, or by being squeezed between rotating units consisting of two cylindrical or conical rollers with a peripheral velocity equal to the desired velocity for casting the thread. When utilizing rotating rollers for the casting operation, the thread is subjected to the acceleration, and not the loop as in the case of a lever, and the loop will shape by itself as a result of the tension of the strand held.
The invention relates in particular to an improvement of the procedure utilizing rotating rollers for casting the weft thread in the shape of a loop.
The main problem to solve in order to implement this procedure is the problem of the shaping of the loop. This is difficult to achieve and depends on the thread acceleration. As a matter of fact, when the startup is fast, the shaping of the loop is excellent due to the massive forces of the thread unwinding, however the startup tensions are excessive. If, on the other hand the startup is slow, the tensions are low, but the loop is fed by a thread going at an accelerated rate which comes into contact with the portions of the thread cast previously at a lower speed. It then shapes into a bale or ball, which increases the air resistance and makes the thread collapse.
Furthermore, it is difficult to regulate the sliding of the thread and apply an adequate acceleration, because of the variations of thicknesses and of the condition of the threads' surfaces.
To compensate for these disadvantages, several systems have been offered, for instance to accelerate the thread before the formation of a loop, and to recover the length of the thread unwound during the acceleration, for the thread which will be cast later on. Another suggestion has been made: to stretch the loop during its formation by means of a jet of compressed air. But all these procedures are complicated and costly.
In most of the known systems which utilize rotating rollers for casting the thread, both rollers are set apart for an instant in order to feed the thread to be cast, they are then brought together closely to hold the thread and pull it. This solution presents some difficulties. One of the two rollers at least must be able to complete a movement of translation perpendicular to its axis in order to be moved away from the other roller, so that the thread can be inserted. Furthermore, since the rollers must have the same outer speed to minimize the friction and position the thread in a well defined direction, the fact that the rollers must be separated for a while therefore requires that both be driven into motion. Moreover, the loop must be prepared in advance, which necessitates an additional mechanism. Finally, since the strand cast between the rollers is directly subject to a maximum friction resulting from the outer speed of the rollers, the thread is being worn out at that point while the acceleration which results therefrom, and which is difficult to control, develops a high thread-tensioning.
According to this invention, the process aims at eliminating these disadvantages.
In a general manner, the invention therefore relates to a process for inserting a weft thread into the space between two layers of warp threads forming the shed in a weaving loom, and the steps of this process are as follows:
storing, in a storage space, a specific or predetermined length of weft thread with one end free,
stopping the accumulated thread at a point situated at a distance measured from the free end of the thread, and which must be equal at least to the pick of weft thread to be inserted,
casting the thread in the shape of a loop into the space between the two layers of warp threads, said loop having one cast strand and the casting being produced by squeezing and one locked strand, the thread between two casting rollers which rotate in opposite directions and which are positioned between the locking point of the locked strand and the free end of the cast strand so that the kinetic energy of the cast strand produces a force pulling the thread from where it unwinds. According to the invention the insertion of the thread between the casting rollers takes place by lateral change of position of the said thread between a guiding point situated upstream of the common generatrix of the casting rollers and a locking point situated downstream of said common generatrix so that the weft thread, at the time of the casting operation, is moved laterally in order to insert it within the gripping line of the casting rollers so that, once cast, the thread moves along this line to form a loop between the locking point and the cast strand by driving the specific length of thread out of the storage space.
The moving of the thread into position within the gripping line of the casting rollers may be achieved either by moving the locking point, or by moving the thread to a zone situated between the guiding point and the locking point.
As a result of the lateral change of position of the thread casting, the portion of the thread which picks up speed is not cast against the portion of thread previously cast which is moving more slowly to its one side. Therefore this arrangement allows a proper formation of the loop and decreases the tensions resulting from the acceleration when starting up (surge tension) without the thread sliding between the driving surfaces. As a matter of fact, the startup speed of the thread, when not sliding, will be V.sub.o sin. .alpha., with .alpha. being the angle between the thread considered at the guiding point and the gripping line between the opposed generatrices of the rollers as shown in FIGS. 2 and 3. The startup speed being decreased, the tension will also be decreased. As the thread moves, the angle .alpha. will increase, therefore occasioning an increase of the thread speed. Consequently the thread speed can be accelerated without the thread sliding between the rollers.
The invention also relates to a device to implement the aforesaid process, and this device is equipped as follows:
means to store in a storage space a specific length of thread with one free end,
a pair of casting rollers permitting the casting of the thread in a shape of a loop with one locked strand and one cast strand, inside the space between two layers of warp threads, this loop unwinding, when emerging from the space between two layers of warp threads, due to the effect of the kinetic energy generated at the casting time, the device being characterized as follows:
a guide is placed upstream said rollers and a gripping system is arranged so that the thread may form, between the above-mentioned elements, an angle with the gripping line between these rollers, and be maintained outside of this gripping line before being cast,
there is a system permitting movement of the thread in order to insert it through the rollers between the guide and the gripping system, to cast the thread and shape it into a really tight loop, by drawing out of the storage space the specific length of thread.
If a permanent tangential contact can be achieved between the rollers, with the line between the generatrices common to both rollers constituting the gripping line, it may however be an advantage to make allowance for a very low clearance between the rollers in order to facilitate the casting operation, especially if the thread is relatively coarse, and in particular if the roller surfaces are hard. In this case, the line between the generatrices closest to each roller can constitute the gripping line. If there is a slight running clearance between the two rollers, it may be necessary to set them to rotate independently from each other.